The present invention relates to the fabrication of-semiconductor devices, and more particularly to isolating components in SOI devices.
Semiconductor chips are used in many applications, including as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices. Moreover, it is desirable that the devices operate at very fast speeds.
Among the things that can limit the speed with which semiconductor devices operate is extraneous capacitances in the devices. More specifically, undesired electrical capacitance can arise from the portions of the source and drain regions that overlap the gate region, as well as from the source and drain junctions. To limit junction depth and, hence, to decrease junction capacitance, so-called xe2x80x9csilicon on insulatorxe2x80x9d, or xe2x80x9cSOIxe2x80x9d, technology, can be used in which a layer of oxide is buried in the silicon substrate to act as a stop to dopant diffusion (and, hence, to act as a stop to source/drain junction depth).
To isolate adjacent components on a semiconductor device, isolation regions are formed in the substrate between the components. In the context of SOI devices, the isolation regions are formed prior to source/drain dopant implantation by forming trenches down to the buried oxide layer and then filling the trenches with dielectric. As understood by the present invention, however, because the depth at which buried oxide layers are typically formed in a substrate can be as close as 1000 xc3x85 to the surface of the substrate to limit junction capacitance, at such a depth the isolation trenches can be insufficiently deep to adequately isolate adjacent device components from each other. With the above shortcomings in mind, the present invention makes the critical observation that it is possible to limit the depth of the source/drain junctions in semiconductor devices (and, hence, decrease the junction capacitances) using shallow buried oxide layers, while nevertheless forming isolation regions between adjacent components that are sufficiently deep to adequately isolate the components from each other.
A method for making an SOI semiconductor device includes implanting Oxygen and/or Nitrogen into the substrate in intended isolation regions. The method also includes heating the substrate to cause the Oxygen and/or Nitrogen to diffuse and interact with the substrate to establish isolation regions, such that the isolation regions extend from the surface of the substrate to below the buried oxide layer of the SOI device. After forming the isolation regions, source and drain regions can be conventionally formed.
In a preferred embodiment, the heating act includes annealing the substrate. In this embodiment, to promote a uniform Oxygen concentration in the isolation regions, the Oxygen can be implanted using an implantation energy that increases over time. The substrate can also be annealed in an oxygenated ambient atmosphere to replenish the Oxygen concentration near the surface of the substrate as the Oxygen diffuses into the substrate, to promote a uniform Oxygen concentration in the isolation regions. In still another embodiment, instead of annealing the substrate after Oxygen implantation, the substrate can be oxidized to promote a uniform Oxygen concentration in the isolation regions.
In another aspect, an SOI semiconductor device includes a substrate and plural component isolation regions formed in the substrate. The isolation regions include Silicon and at least one of: Oxygen, and Nitrogen.
In still another aspect, a method for making an SOI semiconductor includes providing a semiconductor substrate that defines a surface and that has a buried oxide layer, and then establishing component isolation regions in the substrate which extend from the surface to below the buried oxide layer.
Other features of the present invention are disclosed or apparent in the section entitled DETAILED DESCRIPTION OF THE INVENTION.